An enzyme immunoassay for the quantitative measurement of pregnant mare serum gonadotropin (PMSG) in equine serum and plasma. The DRG PMSG ELISA Kit is a solid phase enzyme-linked immunosorbent assay (ELISA) based on the sandwich principle. The microtiter wells are coated with a monoclonal antibody directed towards a unique antigenic site of the PMSG molecule.  An aliquot of sample containing endogenous PMSG is incubated in the coated well. After washing a second incubation follows with enzyme conjugate, which is an anti-PMSG antibody conjugated with horseradish peroxidase. After incubation the unbound conjugate is washed off.  The amount of bound peroxidase is proportional to the concentration of PMSG in the sample. Having added the substrate solution, the intensity of color developed is proportional to the concentration of PMSG in the sample.